Ink jet printing apparatus, method of supplying ink and method of recovering ink jet print head

ABSTRACT

The ink jet printing apparatus has an ink moving means for returning almost all of the ink in the sub ink tank to the main ink tank. The method of supplying ink has a first step of returning the ink in the sub ink tank to the main ink tank, a second step of discharging bubbles in the sub ink tank out of the sub ink tank, and a third step of, after the first step, supplying a predetermined amount of ink from the main ink tank to the sub ink tank. The method of recovering the ink jet print head has a first step of returning the ink in the sub ink tank to the main ink tank, and a second step of discharging the ink from the print head by, after the first step, applying an external pressure against any part of the ink supply path.

[0001] This application is based on Patent Application No. 2000-285367filed Sep. 20, 2000 in Japan, the content of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an ink jet printing apparatusthat ejects ink for printing, to a method of supplying ink and to amethod of recovering an ink jet print head. More particularly, thepresent invention relates to an ink jet printing apparatus having an inksupply device for supplying ink to the ink ejecting print head, to amethod of supplying ink for the ink jet printing apparatus and to amethod of recovering the print head thereof.

[0004] 2. Description of the Related Art

[0005] Heretofore, an ink jet printing apparatus that prints on a printmedium by ejecting ink has the advantages of being very silent duringoperation, small in size and inexpensive and thus have found recently awide range of applications. An ink jet print head used in such an inkjet printing apparatus to eject ink onto a print medium for printing areclassed into two types: one that uses a piezoelectric element and theother, called a bubble jet type, which uses an electrothermal transducerto cause a film boiling in ink and eject ink by a force of a generatedbubble.

[0006] A known method for supplying ink to the print head involvesinstalling on a carriage a sub tank capable of accommodating a smallamount of ink and supplying ink to the sub tank from a main ink tank.This method can increase the carriage speed and is thus suited forhigh-speed printing. In addition, because the main tank can have a largecapacity, this method is advantageously applied for a large volumeprinting. There are many constructions proposed for such an ink supplymethod. Among them is a pit-in type in which during a non-printingperiod the sub tank is automatically refilled by a large-capacity mainink tank set at an arbitrary location in the ink jet printing apparatus.Another example construction for such a method has the main ink tankinstalled at other than the carriage of the ink jet printing apparatusand supplies ink from the main ink tank to the sub tank through a tube.In these printing apparatus, the sub tank has a function of temporarilyholding bubbles when air entering the ink emerges as bubbles and therebyminimizing adverse effects on printing.

[0007] As the percentage of the bubbles in the sub tank increases, thereis a possibility that, due to environmental changes such as temperaturevariations at a location of the printing apparatus, the bubble mayexpand and cause the ink to leak out of the print head.

[0008] To deal with this problem a variety of methods have been proposedto reduce or eliminate the bubbles remaining in the sub ink tank. Forexample, one method deaerates the ink contained in the main ink tank.This method requires a step of deaeration and must hermetically enclosethe ink tank during transport or in use. Another method of eliminatingbubbles in the sub ink tank comparatively reduces the volume of the subink tank and eliminates the ink and the bubble from the sub ink tank atthe same time by suction. This method, however, increases the amount ofdiscarded ink. Further, if the amount of bubbles, i.e., the amount ofink, in the sub ink tank is not known, the number of recovery operationsand therefore the amount of discarded ink tend to increase making itnecessary to check the amount of remaining ink in the sub ink tank.

OBJECT OF THE INVENTION

[0009] The present invention has been accomplished to solve theabove-described problems and it is therefore an object of the presentinvention to provide an ink jet printing apparatus with a main tank anda sub tank, a method of supplying ink and a method of recovering an inkjet print head, which offer a simple construction and can reliablyeliminate bubbles while minimizing the amount of discarded ink even whenthe amount of bubbles in the sub tank is not clearly known.

SUMMARY OF THE INVENTION

[0010] To achieve the above objective, the ink jet printing apparatus ofthe present invention comprises; an ink jet print head for ejecting ink,a sub ink tank for temporarily holding the ink to be ejected from theprint head, a main ink tank for holding the ink to be supplied to thesub ink tank, and an ink moving means for returning almost all of theink in the sub ink tank to the main ink tank.

[0011] The method of supplying ink of the present invention is used forthe ink jet printing apparatus, wherein the ink jet printing apparatuscomprises an ink jet print head for ejecting ink, a sub ink tank fortemporarily holding the ink to be ejected from the print head, and amain ink tank for holding the ink to be supplied to the sub ink tank,the method of supplying ink comprises; a first step of returning the inkin the sub ink tank to the main ink tank, a second step of dischargingbubbles in the sub ink tank out of the sub ink tank, and a third stepof, after the first step, supplying a predetermined amount of ink fromthe main ink tank to the sub ink tank.

[0012] The method of recovering the ink jet print head of the presentinvention is used for the ink jet printing apparatus with an ink supplypath, and the method of recovering the ink jet print head comprises, afirst step of returning the ink in the sub ink tank to the main inktank, and a second step of discharging the ink from the print head by,after the first step, applying an external pressure against any part ofthe ink supply path.

[0013] With the ink jet printing apparatus, the method of supply ink andthe method of recovering the ink jet print head according to the presentinvention, because the ink in the sub ink tank is returned to the mainink tank and because the amount of ink to be supplied from the main inktank to the sub ink tank is known, the ink can be prevented fromoverflowing from the sub ink tank when the recovery operation isperformed. A predetermined amount of ink can be injected into the subink tank during the recovery operation.

[0014] Further, in the ink jet printing apparatus of the presentinvention, the ink jet print chip having energy generating elements forejecting ink and a nozzle portion for ejecting ink may be arranged onone of surfaces of the sub ink tank. This construction offers anadvantage, in addition to those described above, of being able toappropriately restore the nozzle portion from clogging.

[0015] Further, in the ink jet printing apparatus of the presentinvention, the main ink tank and the sub ink tank for storing ink may beconnected together through a tube. This construction offers anadvantage, in addition to those described above, of being able torestore the nozzle portion from clogging with a small amount ofdiscarded ink.

[0016] Further, in the ink jet printing apparatus of the presentinvention, the main ink tank for storing ink may be arranged at a heightlower than the ink jet print head. In that case, there is an advantage,in addition to those described above, that the positional differencebetween the main ink tank and the ink jet print head can be utilized asan attitude difference appropriately in returning the ink to the mainink tank during the recovery operation.

[0017] Further, in the ink jet printing apparatus of the presentinvention, the sub ink tank may have a valve to communicate the interiorof the sub ink tank to the external air. By using the positionaldifference between the sub ink tank and the main ink tank, the externalair can easily be taken into the sub ink tank, contributing to theproper discharging of the ink out of the sub ink tank.

[0018] Further, in the ink jet printing apparatus of the presentinvention, the means for discharging the ink out of the sub ink tank maybe one that deforms the sub ink tank. In that case, because the ink canbe discharged properly as the sub ink tank is deformed, the clogging ofthe nozzle portion can be eliminated with a small amount of discardedink.

[0019] Further, in the ink jet printing apparatus of the presentinvention, because the supply of ink to the sub ink tank is done by thepit-in system that connects the sub ink tank to the main ink tank whennecessary, it is possible to easily and properly replace the sub inktank.

[0020] The above and other objects, effects, features and advantages ofthe present invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a schematic diagram showing an ink path from an ink tankto an ink jet print head mounted on the ink jet printing apparatus of afirst embodiment of the present invention.

[0022]FIG. 2 is a schematic diagram showing the ink jet printingapparatus as the first embodiment of the present invention.

[0023]FIG. 3A and FIG. 3B are schematic diagrams showing states of a subink tank installed in the ink jet print head in the first embodiment ofthe present invention, with FIG. 3A representing an initial state andFIG. 3B representing a state after printing.

[0024]FIG. 4 is a schematic diagram showing a print head performancerecovery procedure in the first embodiment of the present invention in astate before the start of this procedure.

[0025]FIG. 5 is a schematic diagram showing the print head performancerecovery procedure of FIG. 4 while in operation.

[0026]FIG. 6 is a schematic diagram showing a sub ink tank of an ink jetprint head in a second embodiment of the present invention.

[0027]FIG. 7A and FIG. 7B are schematic diagrams showing a print headperformance recovery procedure in the second embodiment of the presentinvention, with FIG. 7A representing a state before the start of therecovery procedure and FIG. 7B representing a state while the recoveryprocedure is in operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

[0028]FIG. 2 schematically shows a first embodiment of the ink jetprinting apparatus according to the present invention. As shown in thefigure, this printing apparatus supplies ink to the ink jet print headfrom an ink tank through a tube.

[0029] As shown in the figure, the ink jet printing apparatus of thepresent invention mainly comprises: a housing 1 such as a main frame; amain ink tank 2 having ink tanks 2-1, 2-2, 2-3, 2-4 inserted into arecessed portion 3 formed in a side portion of the housing 1; an ink jetprint head 4 having an ink jet print chip with nozzles for ejecting ink;a carriage 5 removably mounting the print head 4 and scanning it forprinting; sub ink tanks 6 for temporarily storing ink; ink supply tubes7 as ink supply paths for connecting the ink tanks 2-1, 2-2, 2-3, 2-4 ofthe main ink tank 2 to the corresponding sub ink tanks 6; a lead screw 8formed with a spiral groove 13 to reciprocate the print head 4 and thecarriage 5 together as one piece in a main scan direction over a printmedium 14 such as print paper and plastic thin plate; a guide rail 9 forreciprocally guiding the carriage 5; a drive motor 12 for rotating thelead screw 8 through gears 10, 11; and a platen roller 15 for feedingthe print medium 14 to a print position.

[0030] In the ink jet printing apparatus of the present invention, whenjoint portions (not shown) of the ink tanks 2-1 to 2-4 of the main inktank 2 to be inserted into the recessed portion 3 of the housing 1 arenot inserted into the ink jet printing apparatus, they are closed byrubber plugs 2 a for preventing ink leakage. When the ink tanks 2-1 to2-4 of the main ink tank 2 are inserted into the recessed portion 3 ofthe ink jet printing apparatus, the rubber plugs 2 a are pierced by inksupply needles 21 a provided to the printing apparatus in order to drawout ink from the individual ink tanks 2-1 to 2-4. There are ink tanksensors in the ink jet printing apparatus to detect when the ink tanks2-1 to 2-4 of the main ink tank 2 are mounted or dismounted. When theink tanks 2-1 to 2-4 are removed from the printing apparatus, the inksupply tubes 7, 21 are closed to prevent the ink in the ink supply tubes7, 21 from spilling out.

[0031] The ink jet print head 4 is removably mounted on the carriage 5that performs a scanning operation for printing. The carriage 5 isprovided with a printing apparatus side connector pad (not shown) thatconnects to a print head side connector pad (not shown). The sub inktanks 6 for temporarily storing inks communicate with the ink tanks 2-1,2-2, 2-3, 2-4 of the main ink tank 2 through the individual ink supplytubes 7, which function as ink supply paths. The lead screw 8 is rotatedby the forward or backward rotation of the drive motor 12 through thegears 10, 11 to cause the print head 4 together with the carriage 5 toscan over the print medium 14 such as print paper and plastic thinplate. At this time, the carriage 5 is guided along the guide rail 9.Because the spiral groove 13 of the lead screw 8 engages an engagementportion (not shown) of the carriage 5, the scan motion of the carriage 5is performed by the drive motor 12 in the longitudinal direction of theprinting apparatus. The print medium 14 thus printed is fed anddischarged by the platen roller 15.

[0032]FIG. 1 schematically illustrates one of the ink paths from theprint head 4 to the ink tanks 2-1, 2-2, 2-3, 2-4 of the main ink tank 2.The ink is supplied from the main ink tank 2, in which an ink-filled bagis accommodated, through the ink supply tube 7 and a dirt filter 16 inthe sub ink tank 6 into the sub ink tank 6 having the print head 4.

[0033] The print head 4 comprises electrothermal transducers such asheaters which function as an energy generation means to eject ink, and aprint head chip having a nozzle portion made from such a nozzle materialas a resin orifice plate. The heater is applied energy to cause filmboiling in ink to eject the ink from the nozzle.

[0034] In the ink supply tube 7, or the ink supply path, of the printingapparatus of this embodiment, an ink chamber 17 is provided whichtemporarily stores an amount of ink that is injected into the sub inktank 6 during the recovery operation. The sub ink tank 6 has a valve 18that is normally closed but, during the recovery operation, is opened tocommunicate the interior of the sub ink tank 6 to the external air.

[0035] Next, operations for supplying ink and for recovering theejection performance will be explained in the case of this embodiment ofthe printing apparatus of the present invention constructed as describedabove.

[0036] Initially, a sufficient amount of ink 19 exists in the sub inktank 6 as shown in FIG. 3A with only a small amount of air 20 contained.As the printing operation proceeds, air mixes in the ink lowering theink level as shown in FIG. 3B. If the printing is continued in thiscondition, the amount of ink 19 in the sub ink tank 6 becomes verysmall, making it difficult to supply ink to the chip of the print head 4and to meet the desired print quality. It is therefore necessary toexpel the air 20 from the sub ink tank 6 before the condition becomesintolerable. Simply drawing air out of the sub ink tank 6 by suction maycause a trouble. That is, since the ink level in the sub ink tank 6 isnot known, when the ink level is high, there is a possibility, unless anink level sensor is provided, that the air drawing operation may be doneexcessively, drawing out not only the air 20 but also the ink 19.

[0037] To avoid this problem, the sub ink tank 6 needs to be restored toan original state by the procedure shown in FIG. 4 in this embodiment.For this purpose, the print head 4 is first moved to a recovery positionin the printing apparatus. Then, as shown in FIG. 4, the valve 18 in thesub ink tank 6 is opened by using a motor in the printing apparatus or apressing member 18 a such as a protruding material. This allows theexternal air to enter into the sub ink tank 6 to raise the pressure inthe sub ink tank 6 to the atmospheric pressure, with the result that theink in the sub ink tank 6 returns to the main ink tank 2. When the subink tank 6 is emptied of the ink, the ink stops at the filter 16. Thisis explained as follows. Since a meniscus force produced at the nozzleportion of the print head 4 and the filter 16 portion is stronger than anegative pressure generated by an attitude difference such as apositional difference between the print head 4 and the main ink tank 2,the meniscus force of the filter 16 holds the ink. Hence, the ink isheld by the filter 16 and therefore remains in the ink supply tube 7.

[0038] Next, with the valve 18 left open as shown in FIG. 5, the inksupply tube 21 between the ink chamber 17 provided in the ink supplytube 7 and the main ink tank 2 is pressed or clamped by a pressingmember 21 b or any other appropriate means to close the ink supply tube7. Then, by pressing the ink chamber 17 with a pressing member 22provided in the ink jet printing apparatus, it is possible to supply tothe sub ink tank 6 a predetermined amount of ink equal to the volume ofthe ink chamber 17 without sending the ink to the main ink tank 2.

[0039] As a final step, the valve 18 in the sub ink tank 6 is closed andthe ink supply tube 21 and the ink chamber 17 are opened or released.This allows a desired negative pressure generated by the attitudedifference between the sub ink tank 6 and the main ink tank 2 to beapplied to the sub ink tank 6, with the result that the printing can beperformed again. Further, when the valve 18 in the sub ink tank 6 isclosed while the ink is being supplied from the ink chamber 17 to thesub ink tank 6, the internal pressure of the sub ink tank 6 rises,forcing the ink out of the nozzles of the print head 4. The valve 18 isclosed at a timing when the amount of ink forced out is minimum. Thismethod can restore the original ink ejection performance of the printhead from the nozzle-clogged state with a very small amount of discardedink.

[0040] Since, with this method of recovery, the amount of ink to beinjected into the sub ink tank 6 is always constant, it is possible toinject a constant amount of ink into the sub ink tank 6 at desiredintervals according to the volume of the sub ink tank 6 without havingto use any ink level sensor in the sub ink tank 6 or without causing anyink leakage. The recovery of the ejection of the print head 4 can alsobe achieved without discarding ink at all or with a very small amount ofdiscarded ink.

[0041] While the method of supplying a predetermined amount ofpressurized ink from the main ink tank 2 to the sub ink tank 6 involvespressing the ink chamber 17 with the pressing member 22 to pressurizethe ink, the present invention is not limited to this method and variousother methods may be used. Among other methods are the one that directlypresses the main ink tank 2 and the one that injects ink from the inkchamber 17 such as a syringe.

[0042] Thus, with the method of supplying ink in the ink jet printapparatus and the method of recovering the print head in the ink jetprinting apparatus of the present invention, because the amount of inkto be supplied is known, the ink can be prevented from overflowing fromthe sub ink tank when it is supplied from the main ink tank to the subink tank and a constant amount of ink can be injected.

Embodiment 2

[0043]FIG. 6 schematically shows a sub ink tank of the print headaccording to a second embodiment of the present invention.

[0044] As shown in the figure, the sub ink tank 23 has a wall 26 madefrom a flexible rubber member; an ink jet print head 27 having energygenerating elements and nozzles to eject ink such as same members usedin the above embodiment 1; and a support member 28 made from resin tosupport a chip of the print head 27. The support member 28 forms a partof a liquid chamber. While in this embodiment, the sub ink tank 23 usesthe wall 26 made from a resilient rubber member or the like, the presentinvention is not limited to this construction. For example, the wall 26may use a resin film urged by a spring as long as it permits the sub inktank 23 to change its volume and does not adversely affect the inkejection during printing. Although not shown in FIG. 6 of thisembodiment, the construction ranging from the filter 16 to the main inktank 2 is similar to that of the embodiment 1.

[0045] The method of restoring the sub ink tank 23 of the embodiment 2to the original performing state will be described by referring to FIG.7.

[0046] Initially, there is ink 24 and air 25 in the sub ink tank 23, asshown in FIG. 7A. For a recovery operation, the wall 26 made from aresilient member which is provided to the sub ink tank 23 is slowlypressed by a pressing member 30 provided in the ink jet printingapparatus, as shown in FIG. 7B. This forces the ink 24 present in thesub ink tank 23 to be pushed out through the filter 16 toward the mainink tank 2. When the sub ink tank 23 is emptied of ink, the meniscusforce of the filter 16 holds the ink in the ink supply tube 7. In thisstate, as the pressing member 30 is further pushed against the resilientwall 26 of the sub ink tank 23, if the meniscus force at the nozzleportion of the print head 27 is set smaller than the meniscus force atthe filter 16, the meniscus of the nozzle portion is broken allowing theair 25 in the sub ink tank 23 to be discharged through the nozzleportion of the print head 27.

[0047] As the pressing member 30 continues to be pushed from the stateshown in FIG. 7B until the resilient wall 26 fully collapses, the air inthe sub ink tank 23 is discharged almost completely from the sub inktank 23, with only a small amount of air left in it. Then, the inkchamber (not shown) is pressurized, as described in the embodiment 1, tosupply ink toward the sub ink tank 23. At the same time, reducing orreleasing the pressing force of the pressing member 30 acting on theresilient wall 26 permits a predetermined amount of ink to be injectedinto the sub ink tank 23.

[0048] As can be seen from the foregoing explanation, the presentinvention eliminates bubbles remaining in the sub ink tank 6, 23attached to the print head 4, 27 either by the method which firstreturns the ink present in the sub ink tank 6, 23 to the main ink tank 2and then injects the ink into the sub ink tank 6, 23 while at the sametime drawing air from the sub ink tank 6, 23 or by the method whichfirst returns the ink in the sub ink tank 6, 23 to the main ink tank 2,expels the air from the sub ink tank 6, 23 and then injects ink from themain ink tank 2 into the sub ink tank 6, 23. With these methods, sincethe amount of ink or the amount of air present in the sub ink tank 6, 23can be set to an almost constant level each time the recovery operationis performed, there is no need to provide an ink level (amount ofremaining ink) detection mechanism in the sub ink tank 6, 23, the inkcan be prevented from overflowing, and a predetermined amount of ink canbe injected. It is therefore possible to provide an ink jet printingapparatus with an ink supply and ejection performance recoverycapability which has high reliability and high ink injection precisionand produces only a very small amount of discarded ink.

Others

[0049] The present invention achieves distinct effect when applied to arecording head or a recording apparatus which has means for generatingthermal energy such as electrothermal transducers or laser light, andwhich causes changes in ink by the thermal energy so as to eject ink.This is because such a system can achieve a high density and highresolution recording.

[0050] A typical structure and operational principle thereof isdisclosed in U.S. Pat. Nos. 4,723,129 and 4,740,796, and it ispreferable to use this basic principle to implement such a system.Although this system can be applied either to on-demand type orcontinuous type ink jet recording systems, it is particularly suitablefor the on-demand type apparatus. This is because the on-demand typeapparatus has electrothermal transducers, each disposed on a sheet orliquid passage that retains liquid (ink), and operates as follows:first, one or more drive signals are applied to the electrothermaltransducers to cause thermal energy corresponding to recordinginformation; second, the thermal energy induces sudden temperature risethat exceeds the nucleate boiling so as to cause the film boiling onheating portions of the recording head; and third, bubbles are grown inthe liquid (ink) corresponding to the drive signals. By using the growthand collapse of the bubbles, the ink is expelled from at least one ofthe ink ejection orifices of the head to form one or more ink drops. Thedrive signal in the form of a pulse is preferable because the growth andcollapse of the bubbles can be achieved instantaneously and suitably bythis form of drive signal. As a drive signal in the form of a pulse,those described in U.S. Pat. Nos. 4,463,359 and 4,345,262 arepreferable. In addition, it is preferable that the rate of temperaturerise of the heating portions described in U.S. Pat. No. 4,313,124 beadopted to achieve better recording.

[0051] U.S. Pat. Nos. 4,558,333 and 4,459,600 disclose the followingstructure of a recording head, which is incorporated to the presentinvention: this structure includes heating portions disposed on bentportions in addition to a combination of the ejection orifices, liquidpassages and the electrothermal transducers disclosed in the abovepatents. Moreover, the present invention can be applied to structuresdisclosed in Japanese Patent Application Laying-open Nos. 59-123670(1984) and 59-138461 (1984) in order to achieve similar effects. Theformer discloses a structure in which a slit common to all theelectrothermal transducers is used as ejection orifices of theelectrothermal transducers, and the latter discloses a structure inwhich openings for absorbing pressure waves caused by thermal energy areformed corresponding to the ejection orifices. Thus, irrespective of thetype of the recording head, the present invention can achieve recordingpositively and effectively.

[0052] The present invention can be also applied to a so-calledfull-line type recording head whose length equals the maximum lengthacross a recording medium. Such a recording head may consists of aplurality of recording heads combined together, or one integrallyarranged recording head.

[0053] In addition, the present invention can be applied to variousserial type recording heads: a recording head fixed to the main assemblyof a recording apparatus; a conveniently replaceable chip type recordinghead which, when loaded on the main assembly of a recording apparatus,is electrically connected to the main assembly, and is supplied with inktherefrom; and a cartridge type recording head integrally including anink reservoir.

[0054] It is further preferable to add a recovery system, or apreliminary auxiliary system for a recording head as a constituent ofthe recording apparatus because they serve to make the effect of thepresent invention more reliable. Examples of the recovery system are acapping means and a cleaning means for the recording head, and apressure or suction means for the recording head. Examples of thepreliminary auxiliary system are a preliminary heating means utilizingelectrothermal transducers or a combination of other heater elements andthe electrothermal transducers, and a means for carrying out apreliminary ejection of ink independently of the ejection for recording.These systems are effective for reliable recording.

[0055] The number and type of recording heads to be mounted on arecording apparatus can be also changed. For example, only one recordinghead corresponding to a single color ink, or a plurality of recordingheads corresponding to a plurality of inks different in color orconcentration can be used. In other words, the present invention can beeffectively applied to an apparatus having at least one of themonochromatic, multi-color and full-color modes. Here, the monochromaticmode performs recording by using only one major color such as black. Themulti-color mode carries out recording by using different color inks,and the full-color mode performs recording by color mixing.

[0056] Furthermore, although the above-described embodiments use liquidink, inks that are liquid when the recording signal is applied can beused: for example, inks can be employed that solidify at a temperaturelower than the room temperature and are softened or liquefied in theroom temperature. This is because in the ink jet system, the ink isgenerally temperature adjusted in a range of 30° C.-70° C. so that theviscosity of the ink is maintained at such a value that the ink can beejected reliably.

[0057] In addition, the present invention can be applied to suchapparatus where the ink is liquefied just before the ejection by thethermal energy as follows so that the ink is expelled from the orificesin the liquid state, and then begins to solidify on hitting therecording medium, thereby preventing the ink evaporation: the ink istransformed from solid to liquid state by positively utilizing thethermal energy which would otherwise cause the temperature rise; or theink, which is dry when left in air, is liquefied in response to thethermal energy of the recording signal. In such cases, the ink may beretained in recesses or through holes formed in a porous sheet as liquidor solid substances so that the ink faces the electrothermal transducersas described in Japanese Patent Application Laying-open Nos. 54-56847(1979) or 60-71260 (1985). The present invention is most effective whenit uses the film boiling phenomenon to expel the ink.

[0058] Furthermore, the ink jet recording apparatus of the presentinvention can be employed not only as an image output terminal of aninformation processing device such as a computer, but also as an outputdevice of a copying machine including a reader, and as an output deviceof a facsimile apparatus having a transmission and receiving function.

[0059] The present invention has been described in detail with respectto various embodiments, and it will now be apparent from the foregoingto those skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspects, and it isthe intention, therefore, in the appended claims to cover all suchchanges and modifications as fall within the true spirit of theinvention.

What is claimed is:
 1. An ink jet printing apparatus comprising: an inkjet print head for ejecting ink; a sub ink tank for temporarily holdingthe ink to be ejected from the print head; a main ink tank for holdingthe ink to be supplied to the sub ink tank; and an ink moving means forreturning almost all of the ink in the sub ink tank to the main inktank.
 2. The ink jet printing apparatus according to claim 1, whereinthe ink jet print head has an ink jet print chip that has energygenerating elements for ejecting ink and a nozzle portion for ejectingink, and the chip is arranged on one of surfaces of the sub ink tank. 3.The ink jet printing apparatus according to claim 1 or 2, wherein themain ink tank and the sub ink tank for storing the ink are connected toeach other through a tube.
 4. The ink jet printing apparatus accordingto claim 1, wherein the main ink tank for storing the ink is arranged ata height lower than the ink jet print head.
 5. The ink jet printingapparatus according to claim 1, wherein the sub ink tank has a valve forcommunicating the sub ink tank to external air, and the ink moving meansutilizes a positional difference between the sub ink tank and the mainink tank.
 6. The ink jet printing apparatus according to claim 1,wherein the sub ink tank is made from a flexible member, and the inkmoving means is a means for deforming the sub ink tank by pressing. 7.The ink jet printing apparatus according to claim 1, wherein an inksupply to the sub ink tank is accomplished by a pit-in system in whichthe sub ink tank is connected to the main ink tank when necessary. 8.The ink jet printing apparatus according to claim 1, wherein the sub inktank is provided with a filter on the main ink tank side.
 9. The ink jetprinting apparatus according to claim 1, wherein the ink jet print headis removably mounted on the ink jet printing apparatus along with thesub ink tank.
 10. The ink jet printing apparatus according to claim 1,wherein the ink jet print head has, as elements for generating energy toeject the ink, electrothermal transducers that generate thermal energyand thereby cause film boiling in the ink.
 11. A method of supplying inkused in an ink jet printing apparatus, wherein the ink jet printingapparatus comprises an ink jet print head for ejecting ink, a sub inktank for temporarily holding the ink to be ejected from the print head,and a main ink tank for holding the ink to be supplied to the sub inktank, the method of supplying ink comprising: a first step of returningthe ink in the sub ink tank to the main ink tank; a second step ofdischarging bubbles in the sub ink tank out of the sub ink tank; and athird step of, after the first step, supplying a predetermined amount ofink from the main ink tank to the sub ink tank.
 12. A method ofrecovering an ink jet print head used in an ink jet printing apparatuswith an ink supply path, wherein the ink jet printing apparatuscomprises an ink jet print head for ejecting ink, a sub ink tank fortemporarily holding the ink to be ejected from the print head, and amain ink tank for holding the ink to be supplied to the sub ink tank,the method of recovering the ink jet print head used in the ink jetprinting apparatus comprising: a first step of returning the ink in thesub ink tank to the main ink tank; and a second step of discharging theink from the print head by, after the first step, applying an externalpressure against any part of the ink supply path.
 13. The ink jet printhead performance recovering method according to claim 12, wherein thesub ink tank has at least a part thereof formed from a flexible memberso that its volume can be changed to deliver ink by pressurization. 14.The method of recovering the ink jet print head according to claim 11 or12, wherein a meniscus force generated at a filter installed in the subink tank on the main ink tank side is stronger than a meniscus forcegenerated at a nozzle portion of the ink jet print head.